1. Field of the Invention
The present invention relates to a stroke judging device for a 4-cycle engine, which uses an electronic fuel injection system, more particularly to a stroke judgment device for a 4-cycle engine that can accurately carry out stroke judgment even when an intake pipe internal pressure is close to atmospheric pressure (negative pressure is low).
2. Background Art
In a conventional 4-cycle engine using an electronic fuel injection system, stroke judgment is detected with both cam shaft phase and crankshaft phase of the engine. However, in Japanese Patent Publication laid-open No. Hei. 10-227252, a stroke judgment device is proposed that carries out stroke judgment not by detecting cam shaft phase, but based on an interrelationship between crankshaft phase and intake pipe internal pressure. As a result, there is no need to install a cam sensor inside the cylinder head of the engine, which enables reduction in size and weight of the engine.
The above described related art pays particular attention to regular variations in intake pipe internal pressure with two rotations of the crankshaft as one cycle, and if the engine is rotating in a steady state it is possible to judge the stroke because the state of each stroke is reflected in the intake pipe internal pressure.
However, in cases where the throttle is wide open in transient states such as when the engine is started, or in cases where the throttle is wide open in a steady state and the engine is rotating at high speed, the intake pipe internal pressure rises to the level of atmospheric pressure, regardless of the stroke. Because of this, the state of each stroke is not reflected in the intake pipe internal pressure and there is a problem that it is not possible to carry out accurate stroke judgment with only the interaction between the crankshaft phase and the intake pipe internal pressure.
An object of the present invention is to solve the above described problems with the related art, and to provide a stroke judging device for a 4-cycle engine that can accurately judge stroke even when the throttle is wide open and intake pipe internal pressure is close to atmospheric pressure (low negative pressure).
In order to achieve the above described object, the present invention provides a stroke judging device for a 4-cycle engine containing a phase detection means for detecting phase of a crankshaft of the 4-cycle engine, intake pipe internal pressure detection means for detecting pressure inside an intake pipe leading to a cylinder of the engine, and first stroke judging means for judging a stroke based on an interrelationship between detected phase of the crankshaft and detected pressure inside the intake pipe, comprising rotation cycle detection means for detecting respective rotation cycles for each phase of the crankshaft, comparing means for comparing two rotation cycles detected in different specified phases of the crankshaft, second stroke judging means for judging the stroke based on comparison results, and selection means for selecting the first or second stroke judging means.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.